Demand for secondary batteries as an energy source has been significantly increased as technology development and demand with respect to mobile devices have increased. Among these secondary batteries, lithium secondary batteries having high energy density and operating potential, long cycle life, and low self-discharging rate have been commercialized and widely used.
A lithium secondary battery has a structure in which an electrode assembly, in which a positive electrode including a lithium transition metal oxide as an electrode active material, a negative electrode including a carbon-based active material, and a porous separator are sequentially stacked, is impregnated with an electrolyte.
The positive electrode is prepared by coating an aluminum foil with a positive electrode material mixture including the lithium transition metal oxide, and the negative electrode is prepared by coating a copper foil with a negative electrode material mixture including the carbon-based active material.
A conductive agent is added to the positive electrode material mixture and the negative electrode material mixture to improve electrical conductivity of the active materials. In particular, since the lithium transition metal oxide used as the positive electrode active material essentially has low electrical conductivity, the conductive agent is essentially added to the positive electrode material mixture.
However, it is difficult to expect uniform mixing of the active material and the conductive agent due to a difference in particle diameters of the active material and the conductive agent. Thus, a large amount of pores having a diameter of a few μm may be formed in the electrode, because agglomeration of conductive agent particles occurs or segregation of particles occurs due to a difference in particle sizes of the active material and the conductive agent.
Since these pores cause an increase in resistance or a decrease in output of the battery, there is a need to develop a method which may improve these issues.